This invention relates to the production of synthetic seeds. It particularly relates to the encapsulation of asexual embryos with an artificial seed coat effective to maintain viability of the embryo and to permit germination with normal seedling development.
Seeds are normally produced by growing plants as a direct consequence of the sexual process. The normal sexual seed consists of a partially developed embryo in a resting phase, as well as various seed coats and nutritive tissues necessary for transport, food storage, and protection. Such seeds are usually the result of the sexual process, having an association with floral parts and requiring pollination.
The production of artificial seeds by asexual means would have substantial benefits for the seed industry and agriculture, particularly in connection with hybrid plants. A cell from almost any part of a plant can produce an asexual embryo and from it another entire plant which is virtually identical to the original plant. Such asexual reproduction of cross-pollinating plants by seed would essentially eliminate the circuitous hybrid route required for maintaining uniformity and hybrid vigor. This is particularly useful for those species for which conventional hybridization techniques are difficult. Asexual seed reproduction could also serve as a delivery system for genetically-engineered genotypes produced by in vitro techniques. Artificial seeds could be produced year round and in very little space.
Asexual embryogenesis in vivo is a well known phenomenon particurlarly in the Rutaceae, Cactaceae, Celastraceae, Liliaceae, Myrtaceae, Orchidaceae, Rosaceae, and Solanaceae families. Tisserat, et al. Horticultural Reviews, pp. 1-99 (1979). The production of asexual embryos by in vitro techniques has also been widely reported. Al-Abta et al. Ann. Bot., 42, 773-782 (1978); Ammirato, P.V. Bot. Gaz., 135, 328-337 (1974); Litz, et al. Hort Science, 15, 733-735 (1980); McWilliams, et al. Ann. Bot., 38, 243-250 (1974); Mullins et al. Expt. Bot., 27, 1022-1030 (1976); Sangwan et al. Expt. Bot., 26, 868-881 (1975). In vitro-produced asexual embryos differ from in vivo-produced seeds by the absence of seed coats. In the present invention, in virtro-produced asexual embryos can be converted into "seeds" by providing a suitable synthetic seed coat that maintains seed viability and permits germination of the seed.
A method for encapsulating seed embryos has been reported in Newsweek, Nov. 28, 1983, p. 111. The method described therein involves a two-step process for coating a pregerminated embryo. The embryo is first coated with a gelatinous material, calcium alginate, then with an extremely thin layer of biodegradable polymer to prevent the coated seeds from sticking together. This encapsulation technology does not produce a true artificial "seed" because the embryo is pregerminated prior to encapsulation. The method of the invention described herein does form a true "seed" because a nongerminated or quiescent embryo is encapsulated within an artificial seed coat. This is accomplished by encapsulation with a non-toxic, biocompatible, water-soluble coating material in a one-step process.
It is, therefore, an object of the present invention to produce artificial seeds having an asexual embryo encapsulated in an artificial seed coat.
Another object is to provide a method to produce mature embryos via asexual embryogenesis without precocious germination.
It is a further object to provide a synthetic seed coat which will prevent lethal desiccation of the embryo, maintain viability of the seed embryo, dissolve in water, and permit germination of the seed.
Yet another object is to increase the survival rate of the encapsulated embryo.
Other objects of the present invention will be apparent from the following description and claims.